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cooling pump impellers keep failing

I have the dual Sherwood pumps on my Kingscraft, and the impellers on the port engine side keep failing every ~20 hours of run time. I'm guessing there could be a couple of reasons this is happening, but wanted to run it by you guys.
Even with new impellers, the water flow through the engine is pretty low. I'm wondering if this is the cause or the symptom of the problem. I guess I need to check the flow on the output of the pump rather than the exhaust to see if it's pumping enough water. What's the best way to flush the water passages?

Our generator has the Sherwood model R30G-1 water pump and its impeller lasts 120-150 hours. If yours is failing that often I would thoroughly clean every part of the system that you can access, including the strainer, pipe elbows, heat exchanger. Be careful if you use a garden hose that you don't force water into the engine's exhaust ports.

Be sure you're picking up all the broken pieces of the last impellers when you're replacing with a new one. The broken pieces can flow through the system and get caught in elbows which restricts water flow. Also, be sure to lubricate your new impeller with liquid dish soap or dishwasher soap when you're putting it in the water pump. This will prevent wear as it's building initial water pressure.

Be sure you're picking up all the broken pieces of the last impellers when you're replacing with a new one. The broken pieces can flow through the system and get caught in elbows which restricts water flow. Also, be sure to lubricate your new impeller with liquid dish soap or dishwasher soap when you're putting it in the water pump. This will prevent wear as it's building initial water pressure.

Actually this is exactly what happened. I assumed the impellers went bad again, but when I pulled the pump off, I found bits of old impeller blocking the intake. I thought I cleared them out from last time. In any case, I'm replacing the impellers with the Globe run dry impellers. They are actually cheaper than OEM impellers - there doesn't seem to be a down side.

Prior to our purchase the boat sat for a few years. We replaced the impeller and about 20-30 hours later the pump failed.

Half a boat buck later ($500) for a new pump I've started to see a reduction again in the exhaust water outflow... I am fearing a failing impreller... but we've got three spares... it's just a PITA job.